Radioreceiver



Aug. 6, 1929.

Filed Feb. 16 1923 Sheets-Sheet l 6 g F/Lfl. 1

7 l 1 'l l I 1 I l :6 HM TING #4 RECTIFIER OFF RECTIFIER RELAY IND.

l l I l I F GALV 4 I 1 I 1 J RECT 2351 5 AMP AMP.

l l l l L ,A.F.TUNED AMPLFIER RECTIFIER RELAY on RECORDER wveutoz PHOTO-ELECTRDIC CELL RH. RANGER Patented Aug. 6, 1929.

OFFICE.

* UNITED STATES PATENT RICHARD HOWLAND RANGER, 0F BROOKLYN, NEW YORK,ASSIGNOR TO RADIO COR- PORATION OF AMERICA, A CORPORATION OF DELAWARE. 9

' RADIORECEIVER.

Application filed February 16, 1923. Serial No. 619,359.

This invention relates to radio telegraphy and more particularly to amethod and means for eliminating or reducing static or naturalinterference in the reception of radio signals.

, Numerous arrangements have been suggested and used for this purposedepending for example on selective tuning or balancing out the static inopposed portions. The efficacy of such arrangements depends uponchanging the ratio of signal to static or upon securing systems ofsimilar characteristics so that the resulting static wave forms arealike so as to permit their cancellation b opposition. Considerabledifficulty has een encountered in making static eliminator's reliableandmore or less trouble is encountered in all methods at certain times.

The object of the present invention is to rovide an improved systemwhich reduces the difliculty in reading signals when static or naturaldisturbances occur.

The term static used throughout the specification and claims is intendedto cover all forms of disturbances such as may be set up byelectrounagnetic waves of undesired form striking the receiving antennaand, as a result, troublesome interferingsounds are set up in thereceiving apparatus. These sounds have been commonly referred to asstatic, atmospheric disturbances, strays, or Xs, but applicant intendsto use the term static to include all of the above forms.

The natural disturbances or statics appear to he of a heterogeneouscharacter having considerable energy. The resultant currents in thereceiving circuit are of a discontinuous nonuniform character and ingeneral the effect upon a receiving circuit is similar to that whichwouldbe produced by heterogeneous shock excitation. The signal. waves,

however, produce forced oscillations resulting in currents of acontinuous andsubstantially uniform character. The operation of myinvention is based on this characteristic difference and to a largeextent is independent of the actual amount of the undesired energy. v I

In the methods now used the indicator, such as the final receiver orrecorder directly combines the tone or marking of the signal with thenoise or marking of the disturbance. As static is discontinuous the energy is very effective for producing an indication and the known methodspermit it to act in a manner by which it often renders the signalsunintelligible.

In accordance with the present invention the energy of the signal isutilized to op erate a limiting cut off and during this signal periodthe static energy is not integrated and on account of its discontinuousnature ordinarily cannot alter this condition. During the spacingperiods, the static due to its interrupted character actuates theindicatorby producing noise in the receiver or a marking period in therecorder and the signal is interpreted from either of the latter. Staticon account of its energy will also under some circumstances reach thelim iting cut off value but as it is usually of short duration it cannotof itself produce silence in the receiver or a non-marking pe r'iod andfor the same reason during the spacing period it will produce noise or amarking period even if it momentarily opcrates the limiting cut off.

As static may not always give sufficient noise to enable the signal tobe read I find it advantageous to produce a continuous tone in thereceiver and to silence this tone by the received signal energy. Staticmay convert a portion of the tone into noise, but ordinarily will notentirely silence the receiver.

It will be seen that this method of operation reverses the spacesandindicating periods and would be difiicult for a Morse operator toread. This may be obviated by any suitable reversal such as reverseMorse signalling or by reversing the relays of the recorder whenthelatter is used.

In carrying out my invention I utilize an arrangement for cutting offthe indicator whenever the received current is greater than a certainlimiting valve which is substantially the value of the signal current. Imay also utilize an arrangement which also cuts off the indicator whenthe received current is less than a certain value. The reading signal isonly produced when the received energy falls within this band.

The novel features which I believe to be characteristic of my inventionare particularly set forth in the appended claims. The invention itself,however, both as to its construction and mode of operation, to-

' traced by a ray of light froni'the recor nection with the accompanyingdrawings in which Fig. 1 is a diagrammatic view of apparatusillustrating the principle of my in vention,

Fig. 2 shows my invention utilising a particular form of limiting cutoil,

Fig. 3 is a curve showing the galvanometer mirror,

Figs. 4 and 5 show a modification invention utilizing a different type 0iting cut off, and v Fig. 6 is a curve explaining the operation of thisform of limiting cut ell.

In Fig. 1, which is intended to illustrate the principle of, as well asa system in accordance with the invention, 1 is a receiving antennagrounded at 2 and coupled' to a resonant circuit 3, 4: by means ofcoupling coil 5. For receiving continuous waves a source of alternatingcurrent 6 is utilized for modulating the received energy at an audiblefrequency or for beat reception for example. The received currents,which may if desired be passed through radio or audio frequencyamplifiers, are then recti fled. The rectified currents are thenimpressed on a current interrupter or limiting cut off relay which isadjusted so that when current of the magnitude of the normal signalcurrent is impressed thereon the in terrupter opens the next circuit.Various arrangements have been utilized for accomplishing this result,several of which will be more specifically referred to in connectionwith the arrangements hereafter described.

' Whenever the current furnished to the limiting cut oil is less thanthe normal received signal currents or less than a certain minimumvalue, the relay is closed and the currents supplied thereto areimpressed on the transformer 7, and are there rectified and used tooperate an indicator, such as a recorder or telephone. If no static isreceived the indicator will respond to the spaces between the dots anddashes. This may be corrected when necessary by a suit able reversal,such as reversing the transmitter or the relay connected to theindicator.

, hen static is received with the signal currents these added currentscannot, except. under extraordinary conditions 'decrease the signalcurrent below the limiting cut off value and the indication given by thesignalling currents during these periods is seldom affected.

During the intervening periods when no signal currents are impressed onthe limiting cut off, the static received will not opercurrents.

ate the limiting cut off unless it is of the ma 'nitude of thesignalling current. When it is of the magnitude of the signallingcurrent and of short duration, the limiting cut off relay will beoperated and the indicator may be nic-mentraily cut off but as theduration is usually very short as compared with a dt or a dash this canordinarly be distinguished from the effects of signalling As theindications during nonsignalling periods will not be sufiicientlycontinuous for easy reading unless there is considerable static, Ipreferably introduce a continuous audible tone in the system, so thatduring the intervening periods when signal currents are not received tooperate the limiting cut off, a continuous tone more or less interruptedby the static noises will be heard instead of the static noises alone.This made he done for example by means of an audio frequency chopper 8coupled to the antenna; or'in any other suitable manner.

When exceptional static of a duration ate a dot or a dash and of de thesignal current is received during intervening periods between thesigrwill operate the cut off and cause the same eifcct as a signal, butit will be noted that is not integrated and cannot, enceptunderextraordinary conditions, affect the: nmi'marking given by thesignalling currents.

Fig. 2 shows an arrangement embodying several additional features aswell as a particular type of lim ting cut off relay which does notintegrate the static energy. The arran ement comprises a radio frequencyamplifier,preferably a three electrode vac uum tube connected to theresonant circuit. The modulation frequency supplied is preferably afrequency such as will give a 3,000 cycle beat for example, whichfrequency is doubled by passing the radio frequency through a double orbalanced rectifier 16 and l7. The rectified currents of a pulsation frequency of 6,000 are then amplified by means of a suitable audiofrequency amplifier and the output is impressed on the impulse balanceor balanced rectifier which in itself is a device for reducing theeffects of static. This arrangement, which is more particularlydescribed in my copending application Serial llo. 581,350 comprises twothree-electrode tubes lG and 17 having the grids connected to oppositeends of the secondary of transformer 18 through grid condensers 19 and20 shunted by grid leaks 21 and 22. The middle point of the secondary isconnected to the cathode of the tubes and the plates are connectedtogether and to the filament through the plate battery 23 and the coil2+1. This arrangement serves substantially to balance the initialimpulses, but received currents cumulatively decre'asethe output of whenno signal is received.

both tubes, so that the large initial impulses of highly damped staticare substantially balanced, as well as the small initial impulses ofsignals. The sustained impulses, however, gradually increase thenegative charge on each of the grids so that the re sultant platecurrent decreases when a sustained alternating current is impressed onthe grids, but a 6,000 cycle variation occurs in the plate current. Thissuper-audio pulsation of 6,000 is impressed by means of a coupling coil26 upon a galvanometer 25, which may conveniently be of the type used inthe well known oscillograph and be re sponsive to frequencies as high as6,000 and thus possess sufficient flexibility to follow the impulsesimpressed upon it and the deflection may occur at a high frequency or asa sin gle deflection according to the arrangement of the circuit. Inaddition, it is desirable to impress an audible frequency of 1,000 onthe system preferabl by means of a light 27 placed to shine on t 1egalvanometer mirror, which light is interrupted by any suitable means,such as a rotating shutter 28, at the desired frequency. The mirror ofthe galvanometer receives and reflects light on a photo-electric cellwhen the deflection of the mirror is such that the light is reflected onthe aperture of the cell. In this modification the galvanometer and thephoto-electric cell constitute the non-integrating limiting cut offrelay. The recording galvanometer of this type is particularly describedin the patent applications of O. A. Hoxey, Serial Nos. 537,802 filedFebruary 20, 1922 and 544,155 filed March 16, 1922.

The high audible frequency of. 6,000 is selected because it is welladapted for operating the limiting cut-off device. The output of thephoto-electric cell is then preferably passed to an amplifier tuned tothe frequency of light interruption (1,000 cycles). The

audio frequency current of 1,000 cycles is then used to operate a relay,recorder or telephone after rectification.

' It is seen that the recorder receives a current for the spaces betweenthe signal elements. It may be arranged to give a normal. record, i. e.onein Which the marks cor respond to the signal elements in any suitablemanner.

The operation is in, general similar to.

that already described. The 1,000 cycle'fre quency is impressed on thegalvanometer when the signal is coming in as well as when there is nosignal. By suitable adjustment the deflection of the galvanoi'netcr iszero The arrangement is such that under those conditions the light,interrupted 1,000 timesper second, falls on the photo-electric cell asshown in Fig. 3, where the dotted lines indicates the band in which thephoto cell receives light from the galvanom'eter.- When thecurrentcarries the mirror so that the light is beyond or does not reachthis hand, no current is delivered by the photo-electric cell. As thelightstrikes the band an output current of,

1,000 cycles is delivered to succeeding devices. Figure 3 is a curveshowing the re lationship between deflection of the galvanometer asordinates and time as abscissae, the black portions indicating theperiods when the galvanometer mirror is illuminated by the lamp 27 andthe unshaded portions where the illumination is cut off by the revolvingscreen 28. The uniform undulations at B and I) are caused by the 6,000cycle current induced in 26 from the coil 24. In Fig. 3 the firstportion of the diagram shows a space with no signal or static currentpresent. When a dot or a dash is re ceived a rectified current of afrequency of 6,000 cycles is impressed on the galvanometer and theresulting increase in the deflection of galvanometer is such that thelight no longcrstrikes the photo-electric cell, or in other Words, theband of rectification shifted so that no current is delivered by thephoto-electric cell. The second portion of Fig. 3 indicates a dash withno static interference present. In the space following the dash the bandshifts back to the photo cell, but an impulse of static f is present.

This impulse momentarily raises the current to the band where the signaloperates, but does not keep the operation in the upper band long enoughto break up the current delivered by the photo cell. The musical tonemay be somewhat affected but the change will scarcely be noticed in thetelephone. In the fourth portion the received current corresponding tothe dash carries the band off of the photo cell aperture. lVhile thereceived energy is on, the static may from time to time break down theband as indicated by the static impulse f but this will only be forshort periods which on the average will be different from the 1,000cycle note and will be eliminated by the tuning to audible frequency. Asthe energy which gets into this audio tuning device is only that derivedfrom the photo-electric cell there is no possibility of shockexcitation, as large impulses have no way of communicating their energydirectly into the tuned circuit.

Unusually strong static will, of course, affect the system as shown inFig. 3-as f, and f but in a way which will eliminate the 1,000 cycleband with the received energy on or off. Static therefore can never givea marking period by itself, as shown by B and D on Fig. 3, since it isnot of sufficient duration to effect the receiver, other than is shownby Fig. 3. I

This arrangement has a further advantage in the fact that the bandfrequency of 1,000 is independent of the incoming frequency ltlf) inevery way, so that it, as Well as its audio tuning, may be fixed.

The transmitter or the rela s will obviousously be reversed so that thesignal may be read more easily. W

F a and 5 s -ovr arrangements similar to l 2 but using a different typeof limitu" The aucio frequency output of is passed through a doublerectifier. agnetron of the type shown in Hull Patent No. 1.314.091comprising a. heated filament 20 and a plate 30 surrounding the filann lthe limiting cut oil. The Jl cuit is coupled to an quencv after 0 L arelay soul le rectifier are connected enclosi re and a nected to a 500cy oscil ator to produce will give two variations of qucncy amplifier istuned to this iroquency.

the magnetron control coil 31 this will bias prouuce a one-sided 17cintensity If the rectification is sufiiciently strong, the

\1 I amplifier tuned per-ales telephone or recort indicating the curiron? the Wound around the outside o Cfill' the band or read field sothat a 1,000 cycle var are "onward on the control and the 500 cycleoscillator will which Will depend on the relat signal.

field or and by coil 31 will prevent the of any plate-filament current.Neither the signals nor the audio tone will then beyond the magnetron.Even if the addition of rectified signals is not sufiicientto actuallycut oil the curr nt in the plate circuit, the rectified curl will causethe magnetron to operate on one side 01" the characteristic curve sothat the tone will be chanced upon the addition of rectified als from1,000to 500 and this tone will be greatly reduced in the subsequentcircuits tuned to a frequency of. 1,000. 0 shows characteristic curve ofthe magnetron, ordinates being the plate current and 1e abscissa thecontrol voltage. iVhen the 500 cycles control is applied the controlvoltage varies from V to V and the plate current from T to P. It therectified voltage V is sufiiciently strong to carry the magnetron.substantially above the cut-oil poin then ii a added 500 cycle controlvaries the voltage from V, to V and the plate current is cut offcompletely. 11'? the rectified signal voltage is V, the superimposed 500cycle voltage causes variation of control voltage from V to V so that a500 cycle variation of plate current results which is greatly decreasedby the subsequentcircuit tuned to 1,000 cycles.

In this system as in the-photo cell arrangement described, no efii'ectis produced dire ly in the second audio tuning by the tone produced iythe signal or static as some high audible frequency is selected formodulation. For example, 3,000 cycles which after double rectificationbecomes 6,000. All that static may do is to raise the control current inthe magnetron to such a point that, the 1,000 frequency tone produced bythe local 500 cycle oscillator is reduced. ()n. account oi? the highperiod used, the of static will not be very prolonged so mat large partof the static W'll produce effects of such a short duration as notaffect the 1,000 cycle note to any great ex- Only under very rareconditions can tent. static produce the r-ceding note 01 1,000 cycleswhen the signal is on, as the times when static would oppose the signalsfor a time interval commensurate with the audio o of 1,000 cycles wouldbe very seldom. the arrangement of Fig. 5 a tube is if similar to themagnetron of Fig. 4. i. the external coil 31 a control e the tube isused for varying rent and as the plate current ey as that of the appliedemf, a 1,000 cycle local oscillator is utilized in place of the 500cycle oscillator. Therectii frequency of 6,000 is applied to H a lcontrol coil 31. In this case the gnetic control would be polarized to apoint a just above the lower cut off limit,

;c that the addition of any opposed rectified signals will carry it backto Z) and cut off the etl'ect ot the audio oscillator on the plate whichis connected to the tuned amplitier as for the magnetron. The action ofthis arrangement for static and signal Would be very similar to themagnetron arrangement of nig. 4.

Having described my invention, What I claim is:

1. The method of receiving radio signals through static, which consists,in receiving radio signals and static, in normally producing observableeffects from the receipt of static energy during non-signalling periodsand in 'nterrupting the said observable effects upon receipt of desiredincoming signal energy and static sii'nultaneously.

2. The method of receiving radio signals through static, Which consists,in receiving signals and static, in producing observable efiects fromstatic pulses alone in the absence of received signals, in preventingthe production of said observabl efiects due to said static duringperiods when signals of the desired character are received jointly withsaid static effects, and in interpreting the desired signals from theabsence of said observable eiiects during periods when both static andsignals are being received.

ed by means of this grid at the 3. A method of receiving radio signalsthrough static,which consists, in normally producing observable effectsfrom static disturbances at periods when signals areinterrupted, ininterrupting production of said. observable effects during periods whensignals and static are received simultaneously, and in interpreting thedesired signals by the absence of said observable effects as interruptedby the simultaneous reception of signals and static. T a

4. The method of receiving radio signals through static which comprisescausing received static energy to actuate an indicatorunresponsive tosignal oscillations, and ren dering said indicator unaffected by saidstatic during periods when desired signal oscillations are received.

5. The method of receiving radio signals through static, which consists,in normally receiving signals and static, in actuating an indicator byreceived static during nonsignalling periods, in causing desired signalsreceived simultaneously with said static to prevent the actuation ofsaid indicator, and in interpreting desired signals by the absenceot'any indication during periods when signals are received. i

6. The method of receiving radio signals through static which consistsin producing at the receiving station a substantially continuous efiectnormally observable during static periods, and in causing the desiredreceived signals to render said efl'ect substantially unobservable.

7. The method of receiving radio signals through static, which consists,in receiving both signals and static, in producing observable effects bythe receipt of said static, in producing a. different observable effectat the receiving station during periods when static disturbances arereduced in, intensity, and in rendering said eil'ects unobservableduring periods when desired signals are received simultaneously withsaid static disturbances.

8. The method of receiving'radio signals through static which consistsin si ultaneously receiving signals and static, and in causing saidreceived signals of predetermined strength to prevent response'in anindicator normally unresponsive to signal.- ling oscillations andnormally responsive to static disturbances, whereby the said static willproduce an. observable effect on said indicator only during intervalswhen signalling oscillations are interrupted.

9. The method of receiving radio signals through static which consistsin simultaneously receiving both static disturbances and transmittedsignals, producing a response by said received static in an indicatorunresponsive to signalling oscillations but normally responsive to saidstatic, introducing into said indicator a substantially continuouseffect observable by means of said indicater during periods when nosignalling os- 'cillations or static are recelved, and in causing saidreceived signalling oscillations to render said indicator normallyunresponsive to both said static'and said continuously said indicator torespond to static disturbances received alone, and to be unresponsive tostatic disturbances .when received simultaneously with receivedsignalling oscillations, v i

12. In a radio receiving system, the combination 01"" a signal receivingcircuit for receiving both static disturbances and desired signallingoscillations, an indicating means for indicating both the staticdisturbances and the desired signalling oscillations, and a limitingcut-oil means associated'with said receiving circuit for causing aresponse in said indicator only at periods when the received energyfalls Within predetermined limits so chosen as to normally include onlythe energy of the said static disturbances, whereby the said indicatoris normally responsive only to static disturbances during periods whenthere is an absence of signalling oscillations on the receiver and thesaid indicator is normally unresponsive when both static and desiredsignalling oscillations are received simultaneously.

13. In a radio receiving system, an antenna. circuit, a resonant circuitcoupled therewith for receiving signals of a desired character andstatic disturbances accompanying said desired signals, an'indicatorassociated with said resonant circuit and arranged so as to be normallyunresponsive to determined band, and an indicator actuated by the outputenergy from said limiting cut-oil means and arranged so as to'respondonly to the uni-directional pulses lying within said predetermined band.

15. In radio receiving systems, the combination of a receiving circuitfor receiving desired signalling oscillations and static dis turbancesaccompanying the same, a rectifier for converting static disturbanceswhen received on said receiving circuit in the ab sence of signals intouni-direction pulses of a magnitude normally lying within apredetermined band and for converting desired signalling oscillationsinto uni-directional pulses of a magnitude normally outside saidpredetermined band, an indicator, and galvanometer means actuated bysaid rectifier for rendering said indicator responsive only touni-directional pulses lying within the said predetermined band, wherebythe receipt of said desired signalling oscillations produce an absenceof any recording effect upon said indicator and signals are determinedin an inverse order.

16. In radio receiving apparatus, the com bination of a receivingcircuit, a rectifier associated therewith, a limiting cut-off operatedbythe output of said rectifier, an indicator controlled by said cut-oft,said cut-off being so arranged as to permit said indicator to respondonly to current strengths of a value less than that of a predeterminedvalue of currents normally produced by received signalling oscillationsand to prevent response of said indicator when the current strengths areequal to or greater than the said predetermined value normally producedby received signalling oscillations.

17. In radio receiving apparatus, the combination of a receiving circuitfor receiving desired signalling oscillations and such staticdisturbances as accompany the same, an indicator associated with saidreceiving circuit and arranged so as to be normally responsive only tostatic disturbances and so as to be unresponsive to desired signallingoscillations, means for locally supplying a disturbing effect to whichsaid indicator is responsive, and means for interrupting the productionof said disturbing effects upon said indicator when signallingoscillations are being received, said means being adapted to preventinterruptions when static only is being received.

RICHARD HOXVLAND RANGER.

